Process and apparatus for fabricating precise microstructures and polymeric molds for making same

ABSTRACT

There is disclosed a method and apparatus for producing a polymeric film that accurately replicates a complex mold surface at least a portion of which surface has microstructured or nano-structured dimensions. A polymeric powder is electrodeposited on an underlying mold surface. Then the powder is cured to create a polymeric film. Finally the film is removed from the mold surface.

This application claims the benefit of U.S. provisional patentapplication Ser. No. 60/485,268, entitled “A Process And Apparatus forFabricating Precise Microstructures And Polymeric Molds for MakingSame.”

BACKGROUND OF THE INVENTION

Fabrication of microstructured and nano-structured products known to beof interest in various industries include arrays of structured elementshaving optical applications, such as lenticular lenses, Fresnel lenses,light guides, diffusers, retro-reflective films, micro-lens arrays,brightness enhancement film (BEF) and LED arrays. Other applicationsinclude , biomedical components, micro-fluidic products, tissue culturemedia, micro-electrical-mechanical (MEMS), micro-acoustical, ChemicalMechanical Planerization (CMP), fuel cells, and other geometries thatbenefit from high speed, precision, microfabrication technology thatprovides high volume commercialization at economical cost.

The present invention has novel advantages because mold cost andfabrication time is reduced, which translates to faster scale-up andcommercialization but also benefits from higher manufacturing speed thanthe prior art. The invention also allows the use of a wider range ofmaterials than the prior art, including both thermoplastic, andthermoset polymers, either potentially loaded with other second phase orfiller materials such as, for example, ceramic, glass or metal powders.Such latitude in prior art processing does not exist or createssignificant tool wear. The present invention provides the ability tomicroform materials withstanding higher use temperatures or that becomepolymer composites, having improved mechanical, electrical or opticalproperties which are of significant benefit for some end useapplications, beyond the narrow range of typically used polymers.

The present invention adapts several commercially known techniques toachieve novel results.

In accordance with the present invention, polymeric products can be madeby electrodepositing powdered polymer by means of a variation of theprocess generally known as powder coating. This process, sometimesreferred to as solventless or dry painting, does not require the use ofany liquids and therefore eliminates the problems associated with airentrapment. Powder is applied to the mold from the bottom up eliminatingthe possibility of air being trapped and speed is only limited by themelt time and cure rate of the polymer.

The powder coating industry is well known for coating metal substratesbut has more recently made significant innovations to reduce both thecure temperature and cure time thereby allowing temperature-sensitivesubstrates such as wood and PVC to be coated. Two of the major industryinnovators are Rohm and Haas Morton Powder Coatings (MPC) and DupontPowder Coatings. Some of the typical polymers used for the powdercoating process are acrylics, generally recommended for extremeweather-resistance, epoxy resins for pipe and office furniture,epoxy-polyesters for light fixtures and shelving, polyesters forpaneling, automotive components & garden furniture and silicones forhigh-temperature applications such as barbecue grills.

Application equipment to dispense the powder is quite sophisticated andcomplete systems from companies such as ITW-Gema, and Wagner providecomplete automated systems that apply powder electrostaticly to parts ona conveyer-line and are then cured. Of specific interest is equipmentwhich has been designed for continuous webs such as coil coating. Powderis applied to moving steel coils at relatively high speed (20-30 ftmin.) and thickness of 50-200 microns (0.002″-0.008″) then cured andwound up into rolls. This equipment is substantially similar to whatwould be required to make continuous rolls of microstructured film asdescribed in this application.

Conventional powder coatings are heat cured at temperatures that rangefrom 300° F. and higher. These are useful for fabrication processes thatuse metal molds or high melt temperature polymeric molds, but in somecases there are advantages to using polymeric molds that have lowertemperature stability. For fabrication processes that use lowtemperature polymeric molds, low temperature powder coatings are ofvalue. Of particular interest are some of the recently developed. UVpowder coatings, which can cure in 1-5 seconds at temperatures as low as125-175° F. Low temperature curing powder coatings are also of valuewhen combining different layers of polymers to achieve products thathave specific physical, chemical or optical properties.

Powder particle sizes range from 5-20 microns in diameter but it ispossible to achieve even smaller sizes. The ability to achieve smallparticle sizes is important to some aspects of this invention because insome applications, there is a need to replicate microstructures withhigh aspect-ratios or with very small functional features. In the caseof a high-aspect ratio feature, a mold with a recessed microstructureonly 10 microns wide and 50 microns deep (5:1 aspect ratio) theassociated powder would have to be small enough to fill the recessedopening of the mold.

SUMMARY OF THE INVENTION

The present invention relates to a process and apparatus used tomicrofabricate precision microstructures, nano-structures and themethods of making polymer molds. Typically microstructures areconsidered to be in the range of 0.010 inches (250 microns) to 0.000393inches (1 micron) and nano-structures to be below 0.00000393 inches(0.001 microns). For purposes of convenience only, the phrasemicrostructure as used herein shall be deemed to include those smallmacrostructures requiring precision optical configurations that requireprecise dimensions, angles and surfaces, such as cube-corner reflection;parabolic surfaces for LED's; dihedrals for light guides and othersknown to those skilled in the optics art. In some instances, the presentinvention also has great utility in forming complex patterns of preciseoptical configurations in relatively small macrostructures, in the rangeof 1 mm to 10 mm..

A primary object of the invention is to provide a method and apparatusfor creating a polymeric film that accurately replicates a complex moldsurface at least a portion of which surface has microstructured ornano-structured dimensions.

Another object of the invention is to provide an article comprised of alayer of polymeric material at least a portion of which contains asurface area of a complex array of microstructure of optically precisedimensions.

Another object of the invention is to provide a process for formingmolds that contain microstructured and nano-structured patterns byelectrodeposition of layers of thermoplastic or thermoset polymers (withand without incorporation of second phase materials).

Another object of the invention is to provide apparatus for continuouslyforming thermoplastic or thermoset precision microstructured productsusing either polymeric or metal molds.

Another object of the invention is to continuously form polymericproducts having precision microstructures and nano structures.

Another object of the invention is to provide apparatus and a process toform precision microstructures in polymers with multiple hard or softlayers.

Another object of the invention is to provide polymeric molds andmicrostructured products from commercially available polymer layersrather than custom formulating polymers.

Another object of the invention is to form polymeric precisionmicrostructures with through holes or vias.

In summary, there is provided a method of producing a polymeric filmthat accurately replicates a complex mold surface at least a portion ofwhich surface has microstructured or nano-structured dimensions,comprising the steps of:

(a) electrodepositing a polymeric powder on an underlying mold surface;

(b) curing the powder to create a polymeric film; and

(c) removing the polymer film

In further summary, there is provided an apparatus for continuouslyproducing a web of polymeric film that accurately replicates a complexmold surface at least a portion of which surface has microstructured ornano-structured dimensions, comprising:

(a) means for electrodepositing a layer of polymeric powder onto anunderlying mold surface;

(b) means for effecting a cure of said powder to create a polymericfilm; and

(c) means for facilitating removal of the film from the mold.

In further summary, there is provided an article comprising a polymericfilm having a portion which is a surface area of a complex array ofmicrostructure of optically precise dimensions and wherein said articleis formed by curing a powder which has been electrodeposited against amold surface defining the shape of at least a portion of the article.

An important advantage of the invention is the ability to make polymericmolds as part of the apparatus to form precision microstructures. Sincemany of these powdered polymers and particularly the UV cure version canbe deposited and polymerized into a mold at low cure temperatures, apolymeric mold becomes a faster and less expensive alternative to metalmolds described in prior art.

Such a polymer mold has multiple cost and process advantages. Byfabricating a polymeric mold consisting of high glass transition polymeror thermosetting polymer, it is possible to replicate lower glasstransition polymers using the process described in U.S. Pat. No.4,486,363 or any improved versions of hot polymer embossing without thecost or time required to build large cylindrical metal molds.

Apparatus and methods are disclosed for fabricating a polymeric mold byelectrostatically applying a powdered polymer layer on to a mastermicrostructured pattern. Master patterns can be made by a number ofrecognized methods such as diamond turning, ruling, deep reactive ionetching (DRIE) or other techniques that provide such patterns. Themaster pattern or an electroformed copy of the master pattern can beused to make polymeric copies quickly and inexpensively that can beassembled by tiling methods known in various industries. This assemblyof parts into a larger mold can be used in conjunction with furtherdisclosed assembly apparatus such as die cutting and precisionpositioning equipment to provide larger molds for use in fabricatingmicrostructured products.

It has also been demonstrated that pieces of a polymer film mold can beadhered to a stronger backing such as stainless steel or other suitablesubstrates that would give the composite additional strength anddurability as well as electrostatic conductivity.

Another method to make a polymeric mold would be to provide a small andinexpensive electroformed mandrel to fabricate a polymer mold of anylength or even continuous rolls of such molds by the use of a scaleddown version of the apparatus described in U.S. Pat. Nos. 4,486,363 or4,601,861.

Yet another method to make a polymeric mold would be to first fashion asmall mold as a small continuous belt, then apply a polymer layercontinuously that will provide replication of the small mold to providea mold of any required length.

One of the primary advantages of this technique is that the masterpattern or mold fills from the bottom up as the powder is deposited.Making polymeric molds by embossing as defined in U.S. Pat. Nos.4,486,363 and 4,601,861 requires the viscous polymer to be pushed downfrom the top, trapping air during the process and is limited tothermoplastic polymers. In accordance with the present invention, smallparticle size and, in particular, sub-micron and nano-scale particleshave advantages in filling sub-micron and nano-scale complex features ascompared to the viscosity and surface tension limitations of hot-polymeror liquid replication found in embossing or casting techniques.

Another primary advantage is that the polymer layers can be made fromthermoset or UV curable polymers which have much higher servicetemperature and dimensional stability.

Using any of the above methods to provide a polymeric mold, powderedpolymers available from various industry sources can be used to makeeither individually replicated parts with microstructured patterns orcontinuously fabricated film wound into rolls.

The present invention is a significant enhancement of the typicalformation of conventional powder coating materials, whereinthermoplastic or thermosetting polymers are ground to fine particlessizes and combined with pigments to provide color, and other additivesspecifically designed to ensure adhesion to a variety of differentsubstrates. The present invention allows for the elimination of pigmentsand adhesion promoters thus permitting conventional powder coatingapparatus to electro-deposit pure powdered polymers on to molds, wherethey then can be cured in place and then removed as a continuous film.

Commercially available or custom formulated powdered polymers can beselected based on the final products requirements for physicalproperties, chemical resistance, weatherability, service temperature,refractive index and light transmission among others.

The simplest form of this invention would be to use a powder version ofthe acrylic or polycarbonate polymers used in the prior art (U.S. Pat.Nos. 4,486,363 and 4,601,861), then electrostatically apply the powderinto a mold, cure the layer with the replicated pattern now locked inthe polymer and remove the layer form the mold. Since the need for thesetwo polymers has been well established in the field of optical and otherlight management microstructures, they would be among the preferredembodiments of this invention.

In conjunction with the novel method of making a polymeric mold one ofthe primary advantages of this technique to fabricate microstructuredproducts is that the mold fills from the bottom up as the powder isdeposited. Prior art requires the polymer to be melted and the highviscosity liquid pushed down from the top while trapping air during theprocess and making it more difficult to achieve the levels of precisionrequired in smaller micro and nano-structured precise patterns.

Another primary advantage of using a powder layer to fill the mold isthat the microstructure features typically represent a minoritycross-section of the entire product and can be quickly filled thenlaminated to a thicker backing thus eliminating the need to melt andform the entire substrate. An example of this is Brightness EnhancingFilm (BEF) known in the industry to improve the brightness efficiency ofnotebook computer screens. This film typically is 0.006 inch (150microns) thick with a microstructure having a cross section of typically0.005 inch (12 microns). In accordance with the present invention, theneed to melt and reform 0.006 inch (150 microns) polycarbonate isunnecessary if the features are replicated with powdered polymer, curedand then laminated to the polycarbonate backing.

Another primary advantage is the speed of application and cure speedcompared to prior art. Typical industry speeds for powder coating andespecially continuous powder coating such as for coil coating steelsheet can be 20-30 feet per minute (6-9 meters) at width up to 8-10 feet(2.4-3 meters).

An additional advantage is that different powder formulas can be appliedin layers. If a hard outer surface of the microstructure is required thefirst thickness of powder could be nylon or other sufficiently hardmaterials, followed by as many different layers as required. During thecured phase they will all fuse together forming gradients of hardness.The fused multilayer film with the microstructured pattern now locked inis now removed from the mold. This layering technique is particularlyuseful for fabricating micro-needles which must be hard enough at thetip to puncture skin but resilient enough at the base not to shear-offunder stress. The same can be done for other physical properties, suchas modulus or resiliency, linear expansion coefficients and tailoredchemical properties such as resistance to acid, caustic, moisturebarrier properties or resistance to solvent-base chemicals.

Yet another advantage is a means to produce precision through-holes inpolymers, or micro-vias, by partially filling a mold leaving the top ofthe microstructures uncovered. The use of a soft polymeric backing-filmcan insure removal of any powder on the tips of the mold and a planersurface on the packed powder. Once cured, the polymer can be removedleaving a precision structured through-hole or via formed by theprojected microstructure in the mold. An additional advantage of thismethod allows the holes to be made in a variety of shapes, such as acircle, triangle, square, etc and tapered to any degree, as determinedby the mold structure.

Still another advantage of this invention also allows microstructures tobe formed onto ridged substrates. Once the mold is filled with thepowdered polymer, it can be laminated to a ridged polymeric sheet andthen cured; thereby fusing the microstructured pattern to a much thickersupport member. An example of this advantage can be demonstrated bylaminating and then fusing clear, polymeric micro-prisms to a thicksheet of ridged clear backing. Typical ranges for the microstructurescould be 64 micron tall micro-prisms (0.0025 inch) fused to 0.375 inchridged sheet. The resulting combination would provide aretro-reflective, micro-prismatic product ridged enough to be a readymade road sign. Normally, micro-prismatic retro-reflective sheeting asdescribed in U.S. Pat. Nos. 4,486,363 and 4,601,861 must be manufacturedwith adhesive backing and then later applied to a treated aluminum panelthat provides a rigid support member. The described novel approachattaches the micro-prisms directly to a polymeric support member such aspolycarbonate or another clear impact resistant polymer; eliminating theadhesive and fabrication operations, significantly reducing cost andfabrication time.

Another advantage of this invention is to use polymer powder directlyfrom the polymerizing process, bypassing the need to form pellets andextrude film. This is of particular advantage for polymers such aspolycarbonate which are first generated as powder, then pellets and thenextruded into film. In the case where some polymers are not normallyproduced as powder, it still may be an advantage to grind the polymerinto powder, rather than extrude pellet into film and then try toreplicate the film.

Another advantage of using powder directly from the reactor is theabsence of additives that are necessary for the extrusion or injectionmolding process that would improve optical properties such as bulkabsorbitivity and light transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

While the drawings depict preferred embodiments of the presentinvention, they are by way of example only and it is not intended tolimit the scope of the invention. It is expected that variations andfurther modifications as well as further applications of the principlesof the invention will occur to others skilled in the art and whilediffering from the foregoing, remain within the spirit and scope of theinvention as described.

FIG. 1 is a schematic edge view of a master pattern, with athermoplastic powdered polymer being applied and cured, providing a filmhaving the master pattern accurately replicated on the film surface;

FIG. 1A is a schematic edge view of a master pattern, with a thermoset,UV curable powdered polymer being applied and cured, providing a filmhaving the master pattern (or mold) accurately replicated on thesurface;

FIG. 2 is an edge view of the cured thermoplastic polymer film beingremoved from the master pattern with the replicated, precisionmicrostructure on the surface;

FIG. 2A is a view similar to FIG. 2 of a UV cured thermoset polymer filmbeing removed from the master pattern with the replicated, precisionmicrostructure on the surface;

FIG. 3 is a perspective view of sections of the replicated polymer filmassembled to make a thin flexible belt to be used as a continuous mold;

FIG. 4 is a side view of the assembled mold sections used as a flexiblebelt driven by rollers;

FIG. 5 is a schematic view of the apparatus to make long lengths ofreplicated polymeric layers to be used as a mold;

FIG. 6 is a schematic view of one form of prior art apparatus being usedto make long lengths of a polymeric mold.

FIG. 7 is a schematic view of the apparatus to make a multi-layeredcontinuous microstructured product;

FIG. 7B is a schematic view of an alternative apparatus to make thecontinuous microstructured product;

FIG. 8 is a schematic view of an apparatus to laminate thin layers ofmicrostructured film to a ridged substrates;

FIG. 8A is a schematic view of an apparatus to laminate thin layers ofmicrostructured film to flexible substrates;

FIG. 9 is a schematic view of the apparatus to make continuousmicrostructured product that consists of multiple polymeric layers;

FIG. 10 is an enlarged view of the different layers in FIG. 9;

FIG. 11 is an enlarged view of the cured layers from FIG. 9 fusedtogether;

FIG. 12 is a schematic view of the apparatus to make continuousmicrostructured product with precision through holes or vias;

FIG. 12A is an exploded view of the composite layers that form theprecision through holes;

FIG. 12B is a plan view of the bottom mold layer and top polymer layerbeing peeled away revealing the fabricated polymer film with precisionthrough-holes;

FIG. 12C is a top down view of the film with through-holes as formed bythe apparatus in FIG. 12;

FIG. 12 D is magnified view of an individual through hole in FIG. C

FIG. 13 is a perspective view of the apparatus to fabricate two-sidedmicrostructured products;

FIG. 14 is an end view of the apparatus to apply addition layers ofpowder coating over the initial electrodeposited layer;

FIG. 15 is a perspective view of the apparatus to apply thick layers ofpowder coating after the initial electrodeposited layer;

FIG. 16 is a perspective view of another apparatus to apply thick layersof powder coating after the initial electrodeposited layer.

DETAILED DESCRIPTION

Referring to FIG. 1, a method to make polymeric mold sections is shownincluding a master pattern 20 made of electrodeposited nickel having arepresentative lenticular microstructure on the surface. Metal molds ortools for producing such devices are well known in the optics art.

An electrostatic gun 21 such as Wagner's Corona PEM-C3 Manual Spray Gunis used to apply a 0.004″ layer of epoxy based 445-100-1 CORVEL® GREENpowder 3 from Rohm and Haas Morton Powder Coatings, with a particle sizeof 10 microns. A source of infra red radiation 22 such as an electric orgas IR emitter at a temperature of 350° F. (176° C.) for two minutes isused to melt and flow the powder 23 which then cures as a polymer film24. The master pattern 20 may be metal or polymeric as long as it isdimensionally stable at the cure temperature required for the polymersbeing applied. One of the primary advantages of using powder to form thepolymeric layer over the master pattern is that it fills the patternfrom the bottom up as the powder is being deposited, eliminating airentrapment, one of the problems common to prior art embossing or castingtechniques.

Normally, substrates that are powder coated are surface treated with anadhesion promoting chemical bath prior to application of the powder toassure adhesion of the powder coating. In this case however since theobjective is to melt, cure and then remove the polymer as a film withthe pattern replicated on the surface 24, the surface treatment of themaster pattern 20 was omitted prior to application of the powder. Inaddition, since most powder coating products are formulated withadhesion promoting additives each product has to be tested to insure itwill separate from the master pattern or mold. In some cases adhesionpromoting additives may be intentionally omitted from a powderformulation if it is found to interfere with the removal process.

The epoxy based 445-100-1 CORVEL® worked well but the process is notlimited to this product. Many other thermoplastics or thermoset powderedpolymers 23 commercially available from suppliers such as Rohm and HaasMorton Powder Coatings or Dupont Powder Coatings are suitable for theprocess. The powder selection and size would be dependant on the end useof the finished product. The suitability of commercially availablepowder coatings for this application is based on several factorsincluding chemical, physical and optical properties, melt point and theability to release from the mold substrate. Among the thermoplastics arepolyesters, acrylics, urethanes, Nylons, polypropylenes, polyethylenes,polyvinylchlorides and silicones. Among the thermosets are epoxies,epoxy- polyesters, and UV curable formulations.

There is a also an unexpected significant advantage in using powderedpolymer produced directly from the polymerizing process and bypassingthe need to extrude film for some microfabrication processes. This is ofparticular advantage for polymers such as polycarbonate which arenormally made as a powder, which is then formed into pellets and thenextruded into film before it is re-melted and pressed into molds.Additionally, other commercially available extrusion grade thermoplasticresins, not normally used for powder coating, such as polycarbonatesfrom GE Plastics or acrylics from AtoFina can be bought in pellet formand ground into powder for electrostatic application such as describedin this application.

Referring to FIG. 2, the epoxy based 445-100-1 CORVEL® cured polymericfilm 24 with the lenticular precision microstructure now replicated onthe surface 25 is easily removable from master pattern 20. Thelenticular precision microstructured pattern 25 has been accuratelyformed on the surface. Moreover, the separated film itself can be usedas a mold to make subsequent replications with lower melt point powders.In this case, the film 5 was 0.004 inches (100 microns) thick.

Microscopic examination of the removed polymer film 24 showed there wasaccurate replication of the lenticular pattern 25 in the polymer whichis flexible enough to handle, bend and itself be used as a mold.

Referring to FIG. 1A the polymeric powder 23 is a clear UV curableproduct designated NX3-9067 Clear, also from Rohm and Haas Morton PowderCoatings. In this case because the cure temperature of the UV curablepolymer 23 is only 175° F. (79° C.), a polymeric master pattern 20 wasused. The polymer master pattern 20 was Auto Haas DR100, an impactmodified PMMA with a precision micro-prismatic structure 26 formed onthe surface. Prior to application of the powdered polymer 23, the masterpattern surface 20 was vapor deposited with an aluminum layer 27 to helpinsure electrostatic charge through the powder coating applicationprocess. Again, for this experiment the use of pretreatments thatsurface etch substrates to improve adhesion of the polymer, was avoided.The powdered polymer 23 was applied in a 0.0010″ (250 microns) thicklayer using a Wagner Corona PEM-C3 Manual Spray gun 2A. The sample washeated with an IR emitter 6A to a temperature of 175° F. (79° C.) fortwo minutes to melt the polymer powder, then cured by UV radiation 8with a 600 watt mercury lamp for two seconds.

The same conditions were also used for a metal substrate made of nickelwith a lenticular microstructure on the surface, the only exceptionsbeing that the vacuum metallized layer was not needed since the metalsubstrate was already conductive.

Referring to FIG. 2A the cured polymeric film 24 with the precisionmicrostructure now replicated on the surface 25 is easily removable frommaster pattern 20 along with the metallized layer 27. Of particularimportance is the replicated accuracy of the UV cured polymer filmremoved from the micro-prismatic, polymeric master pattern. Micro-prismsfunction as precision retro-reflectors if formed within high dimensionaltolerances. Typically, angle tolerances must be held with 2 minutes ofarc or 99.9% of the required geometry, and surface flatness must bewithin 1000 Angstroms or 0.000003″ in order to function properly.Examination of the micro-prismatic structures in the polymer film 24removed from the master pattern demonstrated they were functionalretro-reflectors and therefore dimensionally within the accuracy ofthese tolerances. Moreover, the separated film can be used to makesubsequent replications.

Referring to FIG. 3, a plurality of sections (13 in FIG. 3) of curedpolymeric film 24 with the microstructured pattern 25 are cut andassembled to provide an endless, flexible belt 30 to be used as a mold.

Referring to FIG. 4, the polymeric belt 30 in FIG. 3 is flexible enoughto be used in the path 40 driven by two rollers 41. One preferredembodiment would have the sections adhesively bonded to a strongmetallic or polymeric backing such as stainless steel or Kapton® film 42to improve strength and durability.

The prior art or other equipment used to emboss thin film similar to theequipment herein would include film produced hereby as a mold, asdisclosed in greater detail in U.S. Publication 20030232174 publishedDec. 18, 2003, the subject matter of which is incorporated herein infull by reference.

Referring to FIG. 5, another method to make a polymeric mold of muchlonger length for production apparatus that requires such a mold, is tofirst fabricate a much smaller mold, perhaps 12″ (30.48 cm) in diameteror smaller, to be used as an endless belt 40, which is then replicatedby having powdered polymer 21 applied, melted and cured by 22 using IRheat or UV radiation. The cured film is then removed from the mold, andwound into rolls 28.

Referencing FIG. 6, yet another method to make a polymeric mold of longlength, is by adapting a miniature version of prior art embossingapparatus such as disclosed in U.S. Pat. Nos. 4,486,363 or 4,601,861which can be used to make long lengths of microstructured polymericmolds for use with the apparatus disclosed in this application. Extrudedpolymeric film such as GE 0.006″ (150 microns) polycarbonate 50 alongwith a higher melt point carrier film such as 0.002″ (50 micron) PENN 51is heated by hot roll 52 to a temperature of 425° F. (137° C.). Aplurality (4 in FIG. 6) of pressure rolls 53 at 150 psi (10.5 bar), flowthe polymer into the Fresnel pattern on the metal mold 30 in the path40. The hot film 54 now with the mold pattern transferred to the surfaceis solidified by cooling station 55, removed from the mold 31, thenwound into rolls 28. In this case the embossed film can be used as theunderlying mold surface in the powder technique of the presentinvention.

Referencing FIG. 7, one method to fabricate microstructured products athigher speeds than heretofore available involves use of a polymeric mold30 as illustrated in FIG. 5 or FIG. 6, of considerable length, used inpath 40 of perhaps 100 feet or more. A mold of this size would allow theuse of multiple powder application stations 21 (3 in FIG. 7), to apply alayer of powdered polymer 23, and a plurality (3 in FIG. 7) of curestations 22 to achieve speeds of 50 or 100 ft/min (16 to 33 meters min).A plurality of smoothing rolls 23 (2 in FIG. 7) will speed the flow ofmolten polymer during the melt stage and prior to final cure. Finishedproduct is then removed as a separate and flexible film 31, and thenwound into rolls 28. Speed of the apparatus is limited only by the rateof powder application and length of the IR emitters to melt and cure thepolymer. UV curable polymer would further increase the cure speed andproduce more product per hour with a similar length mold.

FIG. 7B depicts an alternative method of fabricating precisionmicrostructured products using polymeric molds as opposed to metal moldswith prior art apparatus. The machine used was substantially similar tothat described in U.S. Pat. Nos. 4,486,363 and 4,601,861 operating at atemperature of 300° F. (149° C.), a pressure of 150 psi (10.4 bar) and aspeed of 2 feet (61 cm) min. A flexible polymeric film 30 was used in anelliptical path as a mold in the prior art apparatus, in place of themetal mold originally taught. A Fresnel pattern on the surface of 0.0060inch (150 micron) GE polycarbonate was used as the elliptical mold 40 toreplicate the pattern on to 0.005 inch (125 micron) PVC film 50available from Klocker as type PR-180-14. The polymeric mold 30 and the0.005 inch (125 micron) PVC film to be replicated, along with a highermelt point carrier film 0.002 inch (50 micron) PENN 51 are all fed intothe first of four pressure rollers 53. All three films (30,50 and 51)are heated by hot roll 33 while the pressure rolls 53 flow the moltenPVC polymer into the pattern on elliptical mold 30. It should be notedthat the 150° F. (66° C.) temperature is only hot enough to melt thefilm 50 and not the mold 30 or carrier film 51.

The hot film 54, now with the pattern transferred to the surface, issolidified again by cooling station 55. The PVC film 50 and PENN carrierfilm 51 are now removed together from the mold 56, then wound into rolls57.

Microscopic examination of the film 57 removed from the mold 30 showedgood replication of the Fresnel grooves. Using the same machine andconditions, 0.006 inch (150 micron) polysulfone film was scribed withgrove lines of 0.001 inch (25 microns) depth and used as a mold toreplicate the pattern in Auto Haas DR100 impact modified PMMA.Microscopic examination demonstrated good replication of the groovepattern. As a result it was determined that higher melt point polymermolds such as polycarbonate, polysulfone and others can be used as amold to accurately form copies of lower melt point substrates such asPVC, acrylic and other lower melting point polymers.

Referencing FIG. 8, ridged substrates such as 0.375 inch (9.5 mm)polycarbonate sheets 60 can be laminated at roller 61 to the moltenmicrostructured film 62, preheated by IR station 21, and then cured bystation 22. Cured polymer with the microstructured pattern attached thenbecomes an integral part of the finished composite.

Referencing FIG. 8A, a flexible substrate such as 0.006 inch (150microns) polycarbonate 50 can be laminated at roller 51 to the moltenmicrostructured film 52, preheated by IR station 22. Cured polymer withthe microstructured pattern attached at 53 becomes an integral part ofthe finished composite.

Referencing FIG. 9, a method to fabricate a continuous microstructuredproduct consisting of different polymer layers is achieved by usingapplicator gun 70 for the first layer 60, which is cured by IR heatingstation 71. Applicator gun 72 applies the second layer 61, cured by IRheating station 73. Applicator gun 74 applies the next layer 62 which iscured by IR cure station 75 and so on until all required layers areapplied and cured. The final product is then removed from the mold 63and wound into rolls 64.

FIG. 10 is an enlarged side view of the different polymer layers in FIG.9. Applicator gun 40 applied the first layer of powder 41 onto mold 42.The first layer 41 is melted and cured 43 by IR or UV at station 44. Thesecond layer 45 is applied by applicator gun 46 which is melted andcured by IR or UV station 48. The third layer 49 is applied by gun 50which is melted and cured by IR or UV station 52.

Referencing FIG. 11, the layers 53, 54, and 55 have been fused togetherand are removed as one film from mold 56.

FIG. 12 illustrates one preferred method to make precisionmicrostructures with through-holes or vias using a layer of powderedpolymer 57 that is applied onto the mold by gun 58 to some predeterminedlevel so it only partially fills the mold depth after being melted at 59by IR cure station 60. A soft polymer sheet 61 of polyethylene,polyester or similar resiliency then is applied to the surface 61 andpressed into the mold 42 to press the film layer 61 uniformly to somespecific level 63 and then finally cured at by UV or IR station 64. Thesheet 61 then may be removed and separated from the film having the viasformed thereon. The shape of the vias will be determined by the shape ofthe mold protuberances 59.

FIG. 12A is a side view of FIG. 12B illustrating mold 42 being partiallyfilled with polymer 63 and the mold protuberances penetrating the soft,top layer of polymer film.

FIF 12B is a side view of FIG. 12A after cooling with the mold portion65 being peeled away from the bottom of the cured powder coating 59 andthe soft upper film being peeled away from the top 61 of the curedpowder coating 59. The resulting polymer film layer shows through holesaccurately formed as a permanent feature of the replicated film 59.

FIG. 12C is a top down exploded view of the mold 42 as used in FIG. 12and FIG. 12A the polymer layer 66 removed from the mold with precisionthrough holes 67 formed through the polymer.

FIG. 12D is a further exploded view of the through holes 67 shown inFIG. 12C.

FIG. 13 is a side view of apparatus which has demonstrated a capabilityto fabricate two-sided microstructured products. The apparatusconsisting of a double-band press similar to that sold by Hymmen GmbH ofBielefeld, Germany, as models ISR and HPL which are examples ofcontinuous press, high-speed, high-pressure processing machinery. Byincorporating two belts 62 and 65 and individual applicator guns 63 and60, powder coated polymer is electrodeposited on to each belt and thencombined with a thicker backing film 66 laminated between the top andbottom belt 67 fusing the coating deposited on to each belt. The finalproduct, in this illustration is a two-sided microstructured film 68that is wound into rolls 69.

Double band presses of this type can heat and then cool polymersubstrates as thick as 0.25 inches thick (2.54 cm) at high speeds ashigh as 30 to 60 feet per min (10-20 meters min) or more. Apparatus suchas disclosed double-band press is capable of processing temperatures ashigh as 662° F. (350° C.) and pressure as high as 1430 psi (100 bar).The combination of high temperature and high pressure over the entiresurface of the belt makes this apparatus uniquely suited as a means tocontinuously fabricate microstructured and nano-structured polymerlayers.

FIG. 14 is a side view of an apparatus consisting of a positivelycharged screen, which is used to accelerate the powder to achieve highvelocity impact on the surface of the substrate to be coated. It isknown in the powder coating industry that as powder is deposited tothicknesses of 0.005 inches (125 microns) to 0.006 inches (150 microns)and more, the insulating properties of the coating will reduce theability of the coating to be applied to greater thickness because theelectrostatic charge is reduced. Once the initial 0.005 inch (125microns) to 0.006 inch (150 microns) is applied and cured additionalpowder could be applied by the use of an accelerating system to buildthicker layers. This technique could be particularly useful if theinitial coating is warm which helps the subsequent layers to stick tothe first layer.

FIG. 15 is a side view of a mechanical apparatus used to apply thicklayers over the initial electrodeposited powder coating layer. A gravityfeed hopper or similar device 80 applies powder coating 81 over the topof the first powder coated layer 82. A metering knife 83 applies thepowder at a controlled thickness 84 which is then cured by IR or UVstation 85. Both layers are fused together and later removed from mold86..

A powder coating device of this type is used to apply thick layers ofpolymers once the initial layer has covered the micro features and beencured. Since the first electrodeposited layer has now replicated themicrostructures or nano-structures with optical precision the balance ofthe coating can be applied in macro cross-sections and fused to thefirst layer to achieve thickness greater than would normally be doneusing standard powder coating techniques. By this means the processcould achieve thicknesses of several-millimeters if desired.

FIG. 16 is a side view of an alternative mechanical apparatus also usedto apply thick layers over the initial electrodeposited powder coatinglayer. In this case the powder coating is again applied by a hopper 80applies powder coating 81 over the top of the first powder coated layer82. A metering roll 83 is then used to apply a controlled thickness ofthe powder 84 which is then cured by IR or UV station 85

While the invention has been described in conjunction with a preferredembodiment, it will be obvious to one skilled in the art that otherobjects and refinements of the present invention may be made with thepresent invention within the purview and scope of the present invention.

The invention, in its various aspects and disclosed forms, is welladapted to the attainment of the stated objects and advantages andothers. The disclosed details are not to be taken as limitations on theinvention, except as those details may be included in the appendedclaims. The embodiments of the invention in which an exclusive propertyor privilege is claimed are as follows:

1. A method of producing a polymeric film that accurately replicates acomplex mold surface at least a portion of which surface hasmicrostructured or nano-structured dimensions, comprising the steps of:(a) electrodepositing a polymeric powder on an underlying mold surface;(b) curing the powder to create a polymeric film; and (c) removing thepolymer film.
 2. The method of claim 1, wherein the polymeric powdercomprises either a thermosetting resin or a thermoplastic resin.
 3. Themethod of claim 2, wherein the thermoplastic resin comprises one or moreof: acrylic, polycarbonate, polyester, urethane, nylon, polypropylene,polyethylene, polyvinylchloride or silicones.
 4. The method of claim 2,wherein the thermosetting resin is one of the following: functionalepoxy, epoxy-polyester, silicone and UV curable polymer.
 5. The methodof claim 1, wherein the polymeric powder comprises essentially acommercially pure material.
 6. The method of claim 1, wherein thepolymeric powder consists essentially of a commercial pure materialwithout any additives.
 7. The method of claim 1, wherein the polymericpowder includes a further phase or filler material.
 8. The method ofclaim 1, wherein said film is formed continuously by electrodepositingthe powder onto a moving mold surface.
 9. The method of claim 1, whereinthe underlying mold is itself formed of a polymeric material made byelectrodepositing a powder against an underlying substrate having thedesired complex pattern formed therein.
 10. The method of claim 9,wherein the polymeric powder used to form said mold has a higher meltingpoint than the polymeric material used to form said film.
 11. The methodof claim 1, and comprising the further step of adhering said film to afurther film of polymeric material.
 12. The method of claim 11, whereinsaid further film has a different composition and different propertiesthan said first-mentioned film.
 13. The method of claim 11, wherein saidfurther film is adhered in a continuous fashion to said first-mentionedfilm.
 14. The method of claim 11, wherein said further film is made of amaterial harder than said first-mentioned film.
 15. The method of claim11, wherein said further film is adhered by electrodepositing apolymeric powder material to said first-mentioned film and then curingsaid further film.
 16. The method of claim 15, wherein the thickness ofsaid first-mentioned film is between 0.001 inch (25 microns) and 0.020inch (500 microns) and the thickness of said further film is between0.001 inch (25 microns and 0.020 inch (500 microns).
 17. The method ofclaim 11, wherein said first-mentioned film is a UV curable coating,hard thermoplastic such as nylon or polysufone, and the further film ismade of polycarbonate, acrylic or polyurethane.
 18. The method of claim11, wherein said further film is applied by either using a charged moldand powder coating or a coating knife or by coating rollers.
 19. Themethod of claim 1, wherein the particle size of said powder issufficiently small so that the film is formed by filling the patternedrecesses in said mold surface from the bottom up so as substantially toavoid any air entrapment.
 20. The method of claim 19, wherein saidparticle size is no greater than about 50 microns in maximum dimension.21. The method of claim 19, wherein said particle size is in the rangeof about 5-20 microns.
 22. The method of claim 1, wherein the moldsurface is configured to provide throughholes or vias in the removedfilm.
 23. The method of claim 22, wherein said vias are formed by onlypartially filling the depth of the mold with the polymeric powderfollowed by the step of pressing a resilient layer of material to thesurface of the deposited powder to press the powder layer to someuniform level, and then curing the powdered material to form said film.24. The method of claim 1, wherein the curing step is accomplished byeither UV or radiation.
 25. The method of claim 1, wherein the thicknessof said film is between 0.001 inch (25 microns) and 0.020 inch (500microns).
 26. The method of claim 1, wherein said mold is formed of apolymeric material of a high glass transition temperature than thepolymeric product to be formed against said mold.
 27. The method ofclaim 1, further comprising the step of laminating said film to athicker flexible backing material, said laminated flexible materialbeing usable as a mold to form complex microstructural surfaces.
 28. Themethod of claim 1, wherein said mold moves at a speed of between 50 and100 ft./min.
 29. The method of claim 1, wherein the polymeric powder isobtained directly from a polymerizing process and without the need togrind a larger material to provide the powder.
 30. A method of making apolymer film having at least one area of complex pattern of recesses andraised areas above and below the plane of the film, with the patternshapes including at least some of small macrostructure dimensions,comprising the steps of (a) electrodepositing a polymeric powder intothe facing areas of opposed mold faces defining the pattern shapes to beformed; (b) transporting the opposing faces through a cure station wherethe powder is melted and then coated; and (c) stripping the cured filmfrom the opposing mold faces.
 31. The method of claim 30, wherein theelectrodeposited powder is applied to a first mold face, the powder isheated to a flowable condition and a second mold face is applied to saidmolten powder from the opposite side thereof, thereby to provide thecomplex pattern on opposite sides of said film, and then curing andstripping said film from both mold faces.
 32. An article comprising apolymeric film having a portion which is a surface area of a complexarray of microstructure of optically precise dimensions and wherein saidarticle is formed by curing a powder which has been electrodepositedagainst a mold surface defining the shape of at least a portion of thearticle.
 33. The article of claim 32, wherein at least a portion of saidarray includes vias therethrough.
 34. The article of claim 32, whereinsaid article has at least a further layer of polymeric material adheredto said first-mentioned layer.
 35. The article of claim 34, wherein saidfurther layer comprises a polymeric material of a different compositionthan said first polymeric layer.
 36. The article of claim 34 whereinsaid further layer of polymer material is relatively rigid thereby toprovide structural integrity to said article.
 37. The article of claim32, wherein said article comprises a mold for the formation ofadditional articles.
 38. The article of claim 32, wherein said polymermaterial is comprised of a roll of continuous film having repeatingsections of said complex array.
 39. The article of claim 32, whereinsaid mold is formed by assembling a plurality of said articles toprovide a continuous flexible belt having a repeating pattern therein ofsaid complex array.
 40. The article of claim 32, wherein said film has aflexible backing layer therein thicker than said first-mentioned layerto provide strength to said film.
 41. Apparatus for continuouslyproducing a web of film having a complex microstructured ornano-structured pattern in at least a portion thereof, comprising: (a) amold having the microstructured or nano-structured pattern in a surfacethereon; (b) means for electrodepositing a polymeric powder onto saidsurface; (c) means for effecting a cure of said powder to form a filmhaving the desired microstructured or nano-structured pattern thereon;and (d) means for facilitating removal of said film from said mold. 42.The apparatus of claim 41, wherein said mold is of a polymeric materialhaving a higher melt point than the film to be formed thereon.
 43. Theapparatus of claim 41, wherein said mold is in the form of a continuoussurface that passes the means for depositing said powder, thereby toproduce said film on a continuous basis.
 44. The apparatus of claim 43,further including means for electrodepositing a further layer of powderto said first-mentioned layer and means for curing said further layer.45. The apparatus of claim 43, and further including means forlaminating a further relatively stronger and rigid polymer layer ofmaterial to said first-mentioned layer to provide a relatively rigidpolymeric article having the complex microstructure or nano-structuresurface thereon.
 46. The apparatus of claim 41 and further including afurther mold having a pattern complementary to said first-mentioned moldpattern; means for engaging said further mold with said electrodepositedpowder prior to curing same, whereby to produce a film having a patternon both sides of the film.